Consider the following schedule involving two transactions:
S1: r1(A); w1(A); w2(B); w3(C); r1(D); w2(D).
S2:r3(A); w4(B); r1(C); r3(D); w3(B); w2(D); r3(A); w1(D); r3(B); r2(C); r1(A).
A) only S1 is followed under 2PL.
B) only s2 is followed under 2PL.
C) both s1 and s2 are allowed under 2PL.
D) neither s1 nor s2 are allowed under 2PL.